[PATCH] merge.graft: add option to keep second parent

[Augie Fackler]

On Thu, Dec 03, 2015 at 11:57:45PM -0500, Andrew Halberstadt wrote:
> # HG changeset patch
> # User Andrew Halberstadt <ahalberstadt at mozilla.com>
> # Date 1449201719 18000
> #      Thu Dec 03 23:01:59 2015 -0500
> # Node ID 212f93c2367203cadfd6103f444899929b8643ae
> # Parent  71aa5a26162d6e4a165b68f07b331e3e2eedc117
> merge.graft: add option to keep second parent

Queued, thanks. Congratulations on your first hg patch.

>
> Currently merge.graft re-writes the dirstate so only a single
> parent is kept. For some cases, like evolving a merge commit,
> this behaviour is not desired. More specifically, this is
> needed to fix issue4389.
>
> diff --git a/mercurial/merge.py b/mercurial/merge.py
> --- a/mercurial/merge.py
> +++ b/mercurial/merge.py
> @@ -1484,41 +1484,47 @@ def update(repo, node, branchmerge, forc
>              repo.dirstate.endparentchange()
>      finally:
>          wlock.release()
>
>      if not partial:
>          repo.hook('update', parent1=xp1, parent2=xp2, error=stats[3])
>      return stats
>
> -def graft(repo, ctx, pctx, labels):
> +def graft(repo, ctx, pctx, labels, keepparent=False):
>      """Do a graft-like merge.
>
>      This is a merge where the merge ancestor is chosen such that one
>      or more changesets are grafted onto the current changeset. In
>      addition to the merge, this fixes up the dirstate to include only
> -    a single parent and tries to duplicate any renames/copies
> -    appropriately.
> +    a single parent (if keepparent is False) and tries to duplicate any
> +    renames/copies appropriately.
>
>      ctx - changeset to rebase
>      pctx - merge base, usually ctx.p1()
>      labels - merge labels eg ['local', 'graft']
> +    keepparent - keep second parent if any
>
>      """
>      # If we're grafting a descendant onto an ancestor, be sure to pass
>      # mergeancestor=True to update. This does two things: 1) allows the merge if
>      # the destination is the same as the parent of the ctx (so we can use graft
>      # to copy commits), and 2) informs update that the incoming changes are
>      # newer than the destination so it doesn't prompt about "remote changed foo
>      # which local deleted".
>      mergeancestor = repo.changelog.isancestor(repo['.'].node(), ctx.node())
>
>      stats = update(repo, ctx.node(), True, True, False, pctx.node(),
>                     mergeancestor=mergeancestor, labels=labels)
>
> -    # drop the second merge parent
> +    pother = nullid
> +    parents = ctx.parents()
> +    if keepparent and len(parents) == 2 and pctx in parents:
> +        parents.remove(pctx)
> +        pother = parents[0].node()
> +
>      repo.dirstate.beginparentchange()
> -    repo.setparents(repo['.'].node(), nullid)
> +    repo.setparents(repo['.'].node(), pother)
>      repo.dirstate.write(repo.currenttransaction())
>      # fix up dirstate for copies and renames
>      copies.duplicatecopies(repo, ctx.rev(), pctx.rev())
>      repo.dirstate.endparentchange()
>      return stats
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